The objective of this project is to develop and validate a method for measuring workers' exposure to health hazards in the construction industry. Traditional industrial hygiene methods involve the measurement of airborne concentration of a particulate or gaseous contaminant. This approach does not account for the variable rate of respiration of the worker. In construction, where the human work load may vary by a large degree during a shift, and indeed during a single task, this factor is extremely important in determining the workers' dose of inhaled agent. The lack of accurate dosimetric measurements causes uncertainty in exposure assessment for hazards such as asbestos, lead and solvent fumes from painting, as examples. The specific aims of this project are to develop a modified air sampling pump whose flow rate is proportional to the worker's pulmonary ventilation rate, and to test this sampler on construction workers in the field. The sampling pump will use an input signal, derived from either heart rate or thoracic dimensions, to alter the air flow rate. Thus the amount of contaminant collected during the sampling period will be proportional to the mass inhaled by the worker. This contrasts with the traditional constant flow sampling methods which give a result proportional to the average ambient concentration of contaminant. The sampler will first be validated in laboratory experiments in which volunteers will wear the sampler while exercising on a bicycle at rates chosen to simulate work rates on construction jobs. Once validated in the controlled setting, the device will be placed on selected workers at local construction sites where exposure to paint solvents occurs. Performance of the sampler will be evaluated by taking breath samples from the workers at the start of the next shift to estimate absorbed dose. A high correlation between absorbed dose from breath samples, and the physiologic sampler measurement, will demonstrate the effectiveness of the new method.